Squirrel bite—a rare cause of necrotizing soft tissue infection: Case report

Key Clinical Message Although squirrel bites are uncommon and generally benign, they have been implicated in the transmission of certain diseases in humans, some of which can be life‐threatening. This report discusses the case of a 27‐year‐old hunter who developed a necrotizing soft tissue infection with vesiculo‐bullous skin lesions after a ground squirrel bite.


| INTRODUCTION
Domestic animal bites are more common than those involving wildlife.Infections resulting from these bites can lead to severe illness or even death in some instances. 1quirrels are small or medium-sized rodents.They belong to the family Sciuridae which comprises ground squirrels, tree squirrels and flying squirrels. 2Squirrel bites are uncommon and infrequently encountered in medical practice.These rodents have been implicated in the transmission of certain diseases in humans. 3ecrotizing soft tissue infection is an infectious process characterized by rapidly progressive soft tissue destruction with associated systemic toxicity. 4The epidermis, dermis, subcutaneous tissue, fascia and muscle may be affected. 5t is a rare disorder with annual incidence ranging from 0.3 to 15.5 cases per 100,000 population. 6Even with optimal treatment, it is associated with a high mortality rate of 25%. 7Based on microbial etiology, necrotizing soft tissue infection is mainly classified into polymicrobial (type I) and monomicrobial (type II) infections.Polymicrobial necrotizing soft tissue infection is more common and it is caused by aerobic and anaerobic bacteria.The monomicrobial type is often caused by group A Streptococcus and Staphylococcus aureus. 4Factors associated with an increased risk of necrotizing soft tissue infection include recent trauma, intravenous drug use, diabetes mellitus, steroid use, human immunodeficiency virus (HIV) infection, chronic alcoholism, malnutrition, peripheral vascular disease, obesity, liver cirrhosis, and malignancy. 8he clinical manifestations can be varied.Individuals may present with fever, malaise, diarrhea, anorexia and severe pain.Skin necrosis, bullae and ecchymosis can develop in the affected areas of the body.Other clinical features include erythema, edema, and crepitus.Reduced sensation to pain occurs in the affected areas particularly in those with necrotizing fasciitis.This results from thrombosis of small blood vessels and destruction of superficial nerves in the subcutaneous tissue. 4aboratory findings are nonspecific.The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score is a simple tool consisting of six parameters namely total white cell count, hemoglobin, sodium, glucose, creatinine, and C-reactive protein.It is used to distinguish necrotizing infections from other soft tissue infections.A score of ≥6 has been reported to have a sensitivity of 92.9% and a specificity of 91.6% for necrotizing soft tissue infection.Its positive and negative predictive values are 92.0%and 96.0%, respectively. 9,10The details of the LRINEC scoring system are indicated in Table 1.The mainstay of treatment for necrotizing soft tissue infection involves early surgical debridement of necrotic tissue, initiation of broadspectrum empiric antibiotic therapy and hemodynamic support. 11his report discusses a rare case of necrotizing soft tissue infection involving the face, extremities and external genitalia which occurred after a provoked squirrel bite.

| Case history and examination
A 27-year-old hunter with no significant past medical history was brought to the emergency unit of a district hospital in Ghana after a provoked squirrel bite.Five days prior to the presentation, he went out hunting with his dog which caught a ground squirrel.While attempting to take the squirrel away from the dog, his left little finger was bitten by the rodent.He developed a painful, mild swelling at the affected site.He did not seek immediate medical attention but rather applied topical herbal preparation to the site of the bite.Two days later, he had chills, vomiting, nonbloody diarrhea, and generalized weakness.On the third day after the bite, he woke up with blisters on his face, extensor surfaces of the forearms, palms, knees, dorsum of the feet, scrotum, and penis.The blisters on his genitals later ulcerated.The anterior and posterior parts of his trunk were largely unaffected.This was associated with fever, malaise, and moderate generalized body pain.However, there was no itching, mouth sores, odynophagia, ocular pain, discharge from the eyes, dysuria, epistaxis, or bleeding from any part of the body.He continued to use topical and oral herbal preparations but his symptoms did not improve.He denied a history of recent medication use prior to the onset of his symptoms.He had no drug or food allergies.He neither used intravenous drugs nor steroids.He was a former cigarette smoker but did not drink alcohol.
On physical examination, he was acutely ill-looking, febrile (38.8°C), anicteric, not pale, not dyspneic, wellnourished, well hydrated, and had no peripheral lymphadenopathy.He was alert, awake and oriented in time, place and person.His pulse and blood pressure were 136 beats per minute and 109/92 mmHg, respectively.He had a small linear abrasion on the lateral aspect of the left little finger (i.e., the bite site).There were multiple crusted vesicles measuring approximately 0.5 × 0.5 cm on the face (Figure 1A) without oral or nasal ulcers, conjunctival hyperemia or purulent discharge from the eyes.Bilaterally, he had vesicles which measured about 0.5 × 0.5 cm and bullae with sizes ranging from 1.5 × 2.0 cm to 2.5 × 4.5 cm on the extensor surfaces of the forearms, palms, knees, and dorsum of the feet.The palms and feet were mildly swollen, warm to touch and tender with areas of erythema (Figures 2 and 3).There was sparing of the anterior and posterior aspects of his trunk.Also noted was superficial ulceration of the scrotum and the glans penis with overlying black necrotic skin (Figure 4A).There was no crepitation on palpation of the affected areas.Sensation was intact in all the affected parts of the body.

| Methods
Initial laboratory investigations showed neutrophilic leucocytosis, thrombocytopenia, minimally deranged renal biochemistries, elevated C-reactive protein, normal liver biochemistries, and normal urinalysis as well as a negative HIV status.His random blood sugar was 8.7 mmol/L.Table 2 shows the results of the relevant laboratory tests that were done for the patient while on admission.The LRINEC score was 7 (Table 3) which was suggestive of a necrotizing infection.Accordingly, a diagnosis of squirrel bite with necrotizing soft tissue infection was made.
He was started empirically on intravenous clindamycin

Result on day 11 of admission Reference range
Total white cell count (×10 together with infiltration of the bite site with human rabies immunoglobulin as he had been previously vaccinated.Urologist was consulted for urgent debridement of the scrotum and penis (Figure 4B).A sample of necrotic tissue obtained intra-operatively was sent for culture.Daily wound dressing with povidone-iodine was started following debridement.Also, cleansing of the face and other areas with vesiculo-bullous lesions using antiseptic solution was done on daily basis.The patient complained of dizziness, palpitations, and had another fever spike (38.1°C) on the 6th day of admission.Repeat laboratory tests revealed a hemoglobin concentration of 6.3 g/dL.Results of blood and necrotic tissue cultures were negative despite further increases in the white blood cell and neutrophil counts as indicated in Table 2.He was transfused with two units of packed cells.Antibiotic regimen was empirically modified to a triple therapy consisting of intravenous ampicillin 2 g 6 hourly, gentamicin 80 mg 12 hourly and clindamycin 600 mg 8 hourly.

| Conclusion and results
The deranged renal biochemistries, thrombocytopenia, and hyponatremia which were evident from the initial laboratory evaluation had resolved by the 6th day of admission.A repeat complete blood count on the 11th day of admission showed normal white blood cell and neutrophil counts, with the hemoglobin level rising to 10.2 g/dL (Table 2).Over the ensuing days, the patient's condition improved satisfactorily.The crusted lesions on the face completely resolved (Figure 1B).Again, the vesicles and bullae on all the affected parts of his body healed with the dry skin peeling off (Figure 5).There was also gradual re-epithelialization of the debrided scrotum and penis (Figure 4C).He was eventually discharged after 24 days of hospitalization.He was scheduled for regular follow-up at the urology clinic and advised to continue wound dressing on an outpatient basis.At 2-month follow-up after discharge, there was nearly complete re-epithelialization of the penis and scrotum (Figure 6).

| DISCUSSION
In Ghana, squirrels and many other rodents are often hunted for their meat which is commonly served at traditional eateries that sell indigenous Ghanaian foods.Although some studies have suggested that squirrel bites are benign and seldom lead to local or systemic complications, 3,12 a few cases of these bites causing severe illness in humans and even death have been reported.To the best of our knowledge, this is the first reported case of necrotizing soft tissue infection involving the face, extremities, and external genitalia which occurred after a squirrel bite.The soft tissue destruction was mainly limited to the skin and subcutaneous tissue of the patient.
Even though the presence of multiple risk factors substantially predisposes one to developing necrotizing soft tissue infection, 8 it can also occur in healthy individuals who do not have any risk factors 13 as was noted in our patient.In India, a boy was reported to have had necrotizing fasciitis of the left lower limb after a squirrel bite over the dorsum of his left foot. 14Unlike our patient, there were no cutaneous eruptions or ulceration of the penis and scrotum.Aries et al described five patients from Ghana who presented with severe illness following squirrel bites.Three of them died immediately after the presentation.One was a 17-year-old boy who had a febrile F I G U R E 5 Resolution of bullae in the palms with dry skin completely peeled off.
illness which was associated with diarrhea, myalgia, and swollen hands as well as macules and vesicles the face, shoulders and upper arms after his right thumb was bitten by a ground squirrel. 15These clinical manifestations are somewhat similar to those observed in our patient.In contrast to our case, the patient described by Aries et al also had hepatosplenomegaly and epistaxis but there was no perineal or lower extremity involvement.Again, two cases of a pyrexial illness associated with vesiculo-papular skin eruptions occurring after the bite of the ground squirrel were reported in Nigeria. 16Other diseases which have been reported in association with squirrel bites include radial artery pseudoaneurysm, 17 tularemia, 18 anaphylactic shock, 19 rabies, 20 and lymphocutaneous sporotrichosis. 21rompt initiation of broad-spectrum empiric antibiotic therapy after taking a sample for culture, is one of the key principles in the management of necrotizing soft tissue infection.In monomicrobial infections, blood cultures are positive in about 60 percent of cases while in polymicrobial infections, the yield is approximately 20 percent. 4Although culture results were negative in the case of our patient, he responded well to our choice of triple antibiotic therapy.We administered rabies post-exposure prophylaxis to the patient due to a remote risk of rabies transmission via squirrel bites. 20

| CLINICAL LEARNING POINT
Although squirrel bites are mostly benign and infrequently encountered in medical practice, they may lead to necrotizing soft tissue infections which can be lifethreatening.It is therefore advisable for individuals bitten by squirrels to seek medical attention for early detection and prompt treatment of any complication that may occur.

F I G U R E 1 F I G U R E 2
(A) Multiple crusted lesions on the face (B) Complete resolution of facial lesions.Mildly swollen palms with bullae and areas of erythema.F I G U R E 3 Mildly swollen feet with bullae and black necrotic skin overlying the dorsal aspects of the toes.600mg 8 hourly and ceftriaxone 2 g hourly after taking a sample for blood culture.Intravenous fluids, acetaminophen, tramadol, anti-tetanus serum and tetanus toxoid were administered.Additionally, rabies post-exposure prophylaxis was provided by administering 1 mL of rabies vaccine intramuscularly on days 0, 3, 7, 14, and 28 F I G U R E 4 (A) Superficial ulceration of the scrotum and glans penis with overlying black necrotic skin (B) The appearance of the penis and scrotum after surgical debridement (C) Re-epithelialization of the debrided scrotum and penis.T A B L E 2 Results of some laboratory tests for the patient.